The parasympathetic division of the autonomic nervous system (ANS) regulates rest and digestion functions in the body. It works in opposition to the sympathetic division, promoting relaxation, conservation of energy, and digestion. The parasympathetic division consists of preganglionic fibers originating from specific cranial nerves (III, VII, IX, X) and the sacral spinal nerves (S2-S4). These fibers synapse with postganglionic neurons in the terminal ganglia, innervating various organs and tissues.
The sacral part of the parasympathetic division plays a crucial role in regulating the pelvic organs' visceral functions and the large intestine's distal half It is characterized by preganglionic axons originating from the anterior roots of the second through fourth sacral spinal nerves. As these preganglionic axons travel through the sacral spinal nerves, they branch off to form pelvic splanchnic nerves. These nerves synapse with parasympathetic postganglionic neurons in the terminal ganglia present in the walls of the innervated viscera. From these terminal ganglia, parasympathetic postganglionic axons innervate the smooth muscle and glands in the walls of the colon, ureters, urinary bladder, and reproductive organs.
The parasympathetic division influences functions such as:
